Hydrogen as the most efficient and cleanest energy source for fuel cell power is produced by partial oxidation followed by water-gas shift reaction and reforming of hydrocarbons or methanol. Recent works on the preferential oxidation of carbon monoxide in hydrogen rich gases for fuel cell applications are summarized. H2 is used as a fuel for polymer-electrolyte membrane fuel cell (PEMFC). It is produced by reforming of natural gas or liquid fuels followed by water gas shift reaction. The produced gas consist of H2, CO, and CO2. In which CO content is around 1%, which is highly poisonous for the Pt anode of the PEMFC so that further removal of CO is needed. Catalytic preferential oxidation of CO (CO-PROX) is one of the most suitable methods of purification of H2 because of high CO conversion to CO2 at low temperature range, which is preferable for PEMFC operating conditions. Catalysts used for CO-PROX are mainly noble metal based; gold based and base metal oxide catalysts among them Copper-Ceria based catalysts are the most appropriate due to its low cost, easy availability and result obtained by these catalysts are comparable with the conventional noble metal catalysts.
Reference may be made to article in the Int. J. Hydrogen Energy 32: 3880-3886, 2007 by Huang et al. where they used iridium based catalysts (Ir/CeO2) which exhibited excellent performance in PROX process. Reductive pre-treatment of Ir/CeO2 was found to be beneficial to obtain higher CO oxidation activity at low temperatures. The presence of 1.60 wt % of Ir was essential for obtaining high activity in the PROX reaction. The reaction was performed at 80° C. with GHSV 40000 ml g−1 h−1 (2% CO3 1% O2, 40% H2, He) 70% conversion, negligible influence of H2O on activity, CO2 affected negatively.
Reference may be made to article in the Int. J. Hydrogen Energy 32: 3880, 2007 by Huang et al. where they prepared iridium based catalysts (Ir/CeO2) which exhibited excellent performance in PROX process. Reductive pre-treatment of Ir/CeO2 was found to be beneficial to obtain higher CO oxidation activity at low temperatures. The presence of 1.60 wt % of Ir was essential for obtaining high activity in the PROX reaction. The reaction was performed at 80° C. with GHSV 40000 ml g−1 h−1 (2% CO3 1% O2, 40% H2, He) 70% conversion, negligible influence of H2O on activity, CO2 affected negatively.
Reference may be made to article in the Int. J. Hydrogen Energy 35: 3065-3071, 2010 by Zhang et al. where they prepared bi-functional catalyst Ir-FeOx/SiO2, which was active and selective for preferential oxidation of CO under H2-rich atmosphere. Although the activity of the catalyst is good but the reaction temperature was high and the expensive metal like Ir was used as a catalyst.
Reference may be made to article in Appl Catal. A: general 250: 255-263, 2003 by Tanaka et al. where they reported high performance in preferential oxidation of CO in rich hydrogen over K-promoted Rh/USY (K/Rh=3) catalysts. The concentration of CO was below 10 ppm after this process. The addition of potassium to Rh/USY also promoted the activity of CO oxidation without hydrogen. The reaction was performed at 140° C. (75% H2, 0.2% CO3 and 0.2% O2)>99.5% conversion, potassium increases activity of CO oxidation.
Reference may be made to article in Catal B: Environ. 97: 28-35, 210. By Woods et al. where they reported high conversion (≈100% conversion) at high temperature 275° C. But in presence of excess H2 decreases the CO oxidation rate. In this reaction feed was 1% CO, 1% O2, 60% H2, 1% CO2 and GHSV was 30000 ml g-1 h-1.
Reference may be made to article in the Int. J Hydrogen Energy 33: 206-213, 2008 Luengnaruemitchai et al. made a comparative study of synthesized and commercial A-type zeolite supported Pt catalysts for selective CO oxidation in H2-rich stream. The feed composition was 40% H2, 1% CO, 1% O2, 0-10% CO2, 0-10% H2O and temperature was 100-300° C. The conversion was around ˜95%, no effect of CO2 on the conversion. H2O depressed the selectivity and conversion both.
Reference may be made to article in the Appl. Catal. B: environ. 70: 532-541, 2007 Ayastuy et al. used MnOx/Pt/Al2O3 and reported that high CO conversion at high temperature range. 15 wt. % MnOx Pt/Al2O3 was used with 1% CO, 1% O2, 60% H2—He at 160° C., WHSV 12000 h−1 conversion was 100% CO2 enhances activity, H2O inhibits activity with higher MnOx content.
Reference may also be made to article in the Catal. Commun. 9: 1487-1492, 2008 Wang et al. used Au/CeO2—Co3O4 catalysts with a Ce/Co atomic ratio from 0.1 to 0.6 which were prepared by deposition precipitation. CO conversion is 91% while selectivity is around 51% at temperature 80° C.
Reference may also be made to Journal Analytical methods 7: 3238-3245, 2015 where the authors used Cu—CeO2 catalyst to get CO conversion at 180° C. without any addition of excess hydrogen, or H2O or CO2. Although the elemental composition of the catalyst is same (Cu, Ce, O) but the morphology of the catalyst is totally different and this catalyst cannot be used practically for fuel cell operating condition where typical reaction temperature is between 80-120° C. and the feed contains CO, O2, excess hydrogen, CO2 and H2O.
The feed composition was 1% CO, 1% O2, and 50% H2 at with GHSV 30000 ml g−1 h−1. The Cu-based catalysts at relatively low and stable price compared to other platinum group metals, could help reduce the cost of fuel cell technologies. To the best of our knowledge there is not a single report where supported Cu catalyst is used for CO oxidation in presence of excess H2 at low temperatures.